In the description herein, fine metal wires having a thickness of approximately 200 nm or less are referred to as “nanowires”.
Silver nanowires are expected as a conductive material for imparting conductivity to a transparent substrate. By coating a liquid containing silver nanowires (i.e., a silver nanowire ink) on a transparent substrate, such as glass, PET (polyethylene terephthalate), and PC (polycarbonate), followed by removing the liquid component by evaporation or the like, the silver nanowires are in contact with each other on the substrate to form a conductive network, thereby achieving a transparent conductive film. For a transparent conductive material, a metal oxide film represented by ITO has been frequently used. However, a metal oxide film has defects including the high film forming cost, the low resistance to bending, which may prevent the final product from becoming flexible, and the like. A conductive film for a touch-sensitive panel sensor, which is one of the major applications of a transparent conductive film, is demanded to have high transparency and high conductivity, and the demand invisibility thereof is also increasing in recent years. An ordinary ITO film necessarily has an increased thickness of the ITO layer for enhancing the conductivity thereof, but the increase of the thickness may decrease the transparency, and the visibility may not be improved.
Silver nanowires are expected to avoid the aforementioned defects peculiar to a metal oxide film represented by ITO, and have been put to practical use as a material of the transparent conductive film.
Examples of the known synthesis method of silver nanowires used for a conductor of a transparent conductive film include a method of dissolving a silver compound in a polyol solvent, such as ethylene glycol, and depositing metallic silver having a linear shape by utilizing the reduction power of the polyol as the solvent, in the presence of a halogen compound, and PVP (polyvinylpyrrolidone) or a copolymer of vinylpyrrolidone and another monomer, as an organic protective agent (PTLs 1 and 2).